Wireless system with hybrid automatic retransmission request in interference-limited communications

ABSTRACT

A wireless receiver for receiving signals from an interference-limited transmitter in an interference-limited system comprising at least one transmit antenna, wherein the signals comprise a plurality of symbols. The receiver comprises a plurality of receive antennas and collection circuitry for collecting a plurality of signal samples with at least one symbol and interference effects. The receiver also comprises suppression circuitry, accumulation circuitry, circuitry for providing estimates of a group of bits, error detection circuitry and circuitry for requesting the transmitter to transmit a retransmission of a packet in response to detecting an error.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit, under 35 U.S.C. §119(e)(1), of U.S.Provisional Application No. 60/362,123 (TI-34194PS), filed Mar. 6, 2002,and incorporated herein by this reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

The present embodiments relate to wireless communications systems and,more particularly, to interference-limited wireless communicationsystems with packet retransmission in response to detected packet error.

Wireless communications are prevalent in business, personal, and otherapplications, and as a result the technology for such communicationscontinues to advance in various areas. One such advancement includes theuse of spread spectrum communications, including that of code divisionmultiple access (“CDMA”) and wideband code division multiple access(“WCDMA”) cellular communications. In such communications, a userstation (e.g., a hand held cellular phone) communicates with a basestation, where typically the base station corresponds to a “cell.” CDMAcommunications are by way of transmitting symbols from a transmitter toa receiver, and the symbols are modulated using a spreading code whichconsists of a series of binary pulses. The code runs at a higher ratethan the symbol rate and determines the actual transmission bandwidth.Another wireless standard involves time division multiple access(“TDMA”) apparatus, which also communicate symbols and are used by wayof example in cellular systems. TDMA communications are transmitted as agroup of packets in a time period, where the time period is divided intoslots (i.e., packets) so that multiple receivers may each accessmeaningful information during a different part of that time period. Inother words, in a group of TDMA receivers, each receiver is designated aslot in the time period, and that slot repeats for each group ofsuccessive packets transmitted to the receiver. Accordingly, eachreceiver is able to identify the information intended for it bysynchronizing to the group of packets and then deciphering the time slotcorresponding to the given receiver. Given the preceding, CDMAtransmissions are receiver-distinguished in response to codes, whileTDMA transmissions are receiver-distinguished in response to orthogonaltime slots.

In certain prior art packet communication systems as detailed later,packet retransmission is often requested when a received packet isdetected to be in error. This scheme is often referred to as automaticretransmission request (“ARQ”), and ARQ is intended to reduce oreliminate the effects of packet error, as is often desirable in systemswhere packet reliability is of high importance such as in multimediaapplications. Typically, ARQ is achieved by including some type of errorcheck in each transmitted packet, such as a cyclic redundancy code(“CRC”) at the end of a packet and that relates to the data in thepacket. When the packet is received, the receiver decodes the packetand, hence, also the CRC code, further determining from the code whetherthe packet was received without errors. The receiver also has a wirelessfeedback communication link to the transmitter, and in connection withARQ there is often an acknowledgment feedback signal along this linksuch as in the form of one of two complementary signals designated ACKand NACK. If, from the CRC (or alternate code/method), the receiverdetects no errors in a given packet, then the receiver returns an ACKsignal to the transmitter, whereas if the receiver does detect an errorin a given packet, then the receiver returns a NACK signal to thetransmitter. In response to the NACK, the transmitter retransmits thepacket corresponding to the NACK, that is, that packet for which anerror was detected. This retransmission may take place several times fora same packet, where typically there is a limit on the number ofretransmissions, after which the packet is deemed unusable by receiverand as a result the packet is discarded.

Another technology that relates in part to ARQ, and that is also used incertain prior art packet communication systems as detailed later, isreferred to as hybrid ARQ (“HARQ”), where HARQ differs from ARQ in thatHARQ recognizes that error-containing packets may still provide someuseful data at the receiver. In other words, recall from above that thereceiver discards the entire packet under ARQ if, after repeatedretransmissions, an error free packet is not received. In contrast, HARQsystems attempt to extract some or all of the data from packets thathave been deemed to include errors. There are various types of HARQsystems known in the art. One example of a HARQ system is known as Chasecombining. In a Chase combining system, the receiver performs somecoherent combining on multiple received packets that are received asre-transmissions of an originally-transmitted packet. Another example ofa HARQ system is known as an incremental redundancy system. In anincremental redundancy system, the data bits in each retransmittedpacket are the same; however, different encoding bits are used for eachdifferent retransmission. Further, the receiver is made aware of thedifferent encoding schemes and, thus, it attempts to decode eachdifferent packet it receives representing a retransmission in view ofthe encoding bits anticipated to be applied to that packet. The resultsof each such decode are then combined in an effort to accurately predictthe packet data.

Having introduced ARQ and HARQ systems, note that the above introductionalso states that such systems are used in certain prior art packetcommunication systems; in this regard, the present inventors haveobserved that those systems as studied in the literature have beenconfined to additive white Gaussian noise (“AWGN”) or typical fadingchannels. Such systems typically provide a transmitter with a singletransmit antenna and a receiver with a single receive antenna and, thus,the channel between them may be static wherein noise is the primaryvariance, or in the case of the fading channel there may be additionaldiversity due to the fading characteristics. Thus, heretofore, HARQ hasonly been implemented in these types of systems.

More recently there have been developments into wireless communicationssystems that provide additional types of signal diversity and that areoften more practical, but these same systems are interference-limited.In other words, due to the transmitter and/or receiver structure,multiple symbols share the same channel between the transmitter andreceiver and, hence, interference is introduced between differentsymbols communicated from the transmitter to the receiver. As a result,the receiver requires functionality to suppress the interference. Suchsystems are included in many forms. As one example of aninterference-limited system, there are high data rate multiple antennasystems such as multiple-input multiple-output (“MIMO”) systems. In MIMOsystems, each transmit antenna transmits a distinct and respective datastream; the symbols in each stream therefore interfere with the symbolsin the other stream(s), that is, there is spatial interference sincedifferent transmit antennas are used to transmit different data streams.As another example of an interference-limited system, there is theabove-introduced TDMA systems. In TDMA systems, there are frequencyselective channels with long impulse responses; this causes so-calledintersymbol interference (“ISI”), and typically equalizers are used tomitigate the ISI. As yet another example of an interference-limitedsystem, there is the above-introduced CDMA systems. In CDMA, one type ofmultipath interference effect is multiuser interference (“MUI”).Moreover, since CDMA implements orthogonal symbol streams, often theorthogonality reduces ISI to a negligible value and, as a result, oftena less complex receiver structure may be implemented in a CDMA system.However, there is often required a lowering of the spreading factor,that is, the number of modulating chips per transmitted symbol; thisspreading factor reduction also reduces the benefit of orthogonality andconsequently increases the concern for ISI even in CDMA systems. Stillother examples of interference-limited systems can be ascertained by oneskilled in the art, including any combination such as MIMO TDMA or MIMOCDMA.

Given the preceding, the present inventors further recognize that whileHARQ systems have heretofore been described relative to systems withoutinterference, no provision has been made for implementing HARQ into aninterference-limited system. In view of the preceding, therefore, thepreferred embodiments address the drawback of the limited application ofprior art HARQ systems to systems that are not interference limited;further, such prior art systems, while permitting HARQ and therebyobtaining the benefit of increased packet reliability, suffer from alack of speed or throughput as compared to interference-limited systems.As such, the present embodiments endeavor to provide various preferredembodiments representing a combination of HARQ (or a comparablemethodology) with interference-limited systems, as detailed below.

BRIEF SUMMARY OF THE INVENTION

In the preferred embodiment, there is a wireless receiver for receivingsignals from a transmitter in an interference-limited system comprisingat least one transmit antenna, wherein the signals comprise a pluralityof symbols. The receiver comprises at least one receive antenna andcollection circuitry. The collection circuitry is coupled to the atleast one receive antenna and is for collecting a plurality of signalsamples from the at least one receive antenna. The plurality of signalsamples comprise at least one symbol and interference effects betweendifferent symbols communicated from the transmitter to the receiver. Thereceiver also comprises suppression circuitry, coupled to the collectioncircuitry, for suppressing the interference effects. The receiver alsocomprises circuitry for receiving signals from the suppression circuitryand for providing estimates of a group of bits and detection circuitryfor detecting an error in a packet that comprises the group of bits.Lastly, the receiver also comprises circuitry for requesting thetransmitter to transmit a retransmission of a packet in response to thedetection circuitry detecting the error.

Other circuits, systems, and methods are also disclosed and claimed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 illustrates a diagram of a cellular communications system 10 thatis interference limited, and that by way of example could be a CDMA orTDMA system, in which the preferred embodiments may operate.

FIG. 2 a illustrates an electrical and functional block diagram of afirst transmitter 12 according to the preferred embodiment and which maybe used for either or both of base stations BST1 and BST2 in FIG. 1.

FIG. 2 b illustrates an electrical and functional block diagram of asecond transmitter 12′ according to the preferred embodiment and whichmay be used for either or both of base stations BST1 and BST2 in FIG. 1.

FIG. 3 illustrates an electrical and functional block diagram of areceiver 30 ₁ according to the preferred embodiment and for receivingsignals from either of transmitter 12 of FIG. 2 a or transmitter 12′ ofFIG. 2 b.

FIG. 4 illustrates an electrical and functional block diagram of areceiver 30 ₂ according to the preferred embodiment and for receivingsignals from either of transmitter 12 of FIG. 2 a or transmitter 12′ ofFIG. 2 b.

FIG. 5 illustrates a receiver 30 ₂′ as yet another alternative preferredembodiment for receiving signals from transmitter 12 of FIG. 2 a ortransmitter 12′ of FIG. 2 b.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments provide wireless transmissions of symbols froman interference-limited transmitter to a receiver, where the receiverimplements hybrid automatic retransmission request (“HARQ”)functionality. More particularly, therefore, when the receiver receivesa packet of symbols that is found to be in error, the receiver requestsretransmission of the symbol packet; thereafter, the receiveraccumulates those retransmissions as well as operating to suppress theinterference in the received signals. As discussed above in theBackground Of The Invention section of this document,interference-limited systems may take many forms. Thus, by way ofexample the following illustrates a general interference-limited systemwith it understood that the inventive aspects provided below may beemployed in other interference-limited systems.

FIG. 1 illustrates a diagram of a cellular communications system 10 thatis interference limited, and that by way of example could be a MIMO,CDMA or TDMA system, in which the preferred embodiments may operate.Within system 10 are shown two base stations BST1 and BST2. Each basestation BST1 and BST2 includes a respective set of P transmit antennasAT1 ₁ through AT1 _(P) and AT2 ₁ through AT2 _(P) through which eachstation may transmit or receive wireless signals. The general area ofintended reach of each base station defines a corresponding cell; thus,base station BST1 is intended to generally communicate with cellulardevices within Cell 1, while base station BST2 is intended to generallycommunicate with cellular devices within Cell 2. Of course, some overlapbetween the communication reach of Cells 1 and 2 exists by design tosupport continuous communications should a communication station movefrom one cell to the other. Indeed, further in this regard, system 10also includes a user station UST, which is shown in connection with avehicle V to demonstrate that user station UST typically is mobile. Userstation UST includes a multiple number Q of antennas ATU₁ throughATU_(Q) for both transmitting and receiving cellular communications.Lastly, one skilled in the art should appreciate that insofar as system10 and the preferred embodiments apply to various CDMA systems, theyalso apply to WCDMA systems which are a type of CDMA system.

In some respects, system 10 may operate according to known generaltechniques for various types of cellular or other spread spectrumcommunications, including TDMA and CDMA communications. Such generaltechniques are known in the art and include the commencement of a callfrom user station UST and the handling of that call by either or both ofbase stations BST1 and BST2. Where system 10 differs from the prior art,however, is the system for, and method of, performing retransmission ofsymbols by a transmitter in system 10 and receiving and accumulatingthose retransmissions and also suppressing the interference in thosesignals. These distinctions are further detailed below in connectionwith FIGS. 2 through 4.

FIG. 2 a illustrates an electrical and functional block diagram of afirst transmitter 12 according to the preferred embodiment and which maybe used for either or both of base stations BST1 and BST2 in FIG. 1. Invarious respects, transmitter 12 may be constructed according toprinciples known in the art for interference-limited systems, but asfurther detailed below such known aspects are improved as a whole due tothe inclusion within transmitter 12 of the functionality to retransmitsymbols, as a group in the form of a packet, as part of a HARQ operationperformed by a corresponding receiver. In general and as detailed below,transmitter 12 operates to transmit multiple encoded signals to areceiver such as in user station UST of FIG. 1. By ways of example, themultiple encoded signals could include space-time transmit diversity(“STTD”) or orthogonal transmit diversity (“OTD”) signals, and they maybe in either a CDMA or TDMA format Turning more specifically totransmitter 12, from a data processor 13 it receives information bitsB_(i) at an input to a channel encoder 14. Data processor 13 is intendedto represent that bits B_(i) may be provided from various types ofsources. Additionally, and as further detailed below, data processor 13includes a cyclic redundancy code (“CRC”) block 13 ₁ that also adds,typically by appending, a CRC set of bits to groups of bits within dataprocessor 13. These bits, or a comparable technique as may beascertained by one skilled in the art, are used by a receiver thatreceives signals from transmitter 12 to detect errors in the receiveddata. Indeed, if such errors are found, then such a receivercommunicates, via a feedback channel as shown in FIG. 2 a along a dottedline, to an input to data processor 13 so that re-transmission ofcertain bits may be accomplished in response to the receiver receiving apacket of bits and determining from the CRC or the like that thereceived packet includes erroneous data. Channel encoder 14 encodes theinformation bits B_(i) in an effort to improve raw bit error rate.Various encoding techniques may be used by channel encoder 14 and asapplied to bits B_(i), with examples including the use of convolutionalcode, block code, turbo code, or a combination of any of these codes.

The encoded output of channel encoder 14 is coupled to the input of aninterleaver 16. Interleaver 16 operates with respect to a block ofencoded bits and shuffles the ordering of those bits so that thecombination of this operation with the encoding by channel encoder 14exploits the time diversity of the information. For example, oneshuffling technique that may be performed by interleaver 16 is toreceive bits in a matrix fashion such that bits are received into amatrix in a row-by-row fashion, and then those bits are output from thematrix to a symbol mapper 18 in a column-by-column fashion.

Symbol mapper 18 converts its input bits to symbols, designatedgenerally as x_(l). The converted symbols x_(l) may take various forms,such as quadrature phase shift keying (“QPSK”) symbols, binary phaseshift keying (“BPSK”) symbols, or quadrature amplitude modulation(“QAM”) symbols. In any event, symbols x_(l) may represent variousinformation such as user data symbols, as well as pilot symbols andcontrol symbols such as transmit power control (“TPC”) symbols and rateinformation (“RI”) symbols.

Each symbol x_(l) is coupled to a symbol encoder 20, where as introducedabove encoder 20 could be by ways of example an STTD encoder or an OTDencoder. Further while not shown, multiple encoders also may used.Indeed, additional details regarding such alternatives may be found inU.S. patent application Ser. No. 10/107,275 filed Mar. 26, 2002,entitled “Space Time Encoded Wireless Communication System WithMultipath Resolution Receivers,” and hereby incorporated herein byreference. Encoder 20 operates as known in the art and, of coursedepends on the type of encoding implemented (e.g., STTD, OTD), but inthe illustrated example provides a pair of signal outputs. Further,while not shown, in a CDMA implementation, the paired outputs of encoder20 will be spread by a spreading code and then connected to transmitantennas TAT₁ and TAT₂, whereas for a TDMA implementation the pairedoutputs of encoder 20 are connected directly to transmit antennas TAT₁and TAT₂. In any event, from the preceding and for sake of laterreference the output of encoder 20, at a given time (n), may beexpressed as a vector s(n), as shown in the following Equation 1:

$\begin{matrix}{{s(n)} = \begin{bmatrix}{s_{1}(n)} \\{s_{2}(n)}\end{bmatrix}} & {{Equation}\mspace{14mu} 1}\end{matrix}$Further, the symbol vector over a period of time such as encompassing anentire symbol or multiple symbols may be referred to more generally ass. As an additional observation before proceeding, for sake of apreferred embodiment and also as an illustrative example, transmitter 12includes a total of two transmit antennas TAT₁ and TAT₂. However, oneskilled in the art should recognize that many of the inventive teachingsof this document may be applied to transmitters with a number ofantennas greater than two. Additionally, while OTD and STTD systemsimply multiple transmit antennas, note also the either CDMA or TDMA maybe implemented using only a single transmit antenna and, thus, thepreferred embodiments further include such single-transmit antennas intheir scope.

FIG. 2 b illustrates an electrical and functional block diagram of asecond transmitter 12′ according to the preferred embodiment and whichin many respects resembles transmitter 12 of FIG. 2 a, where likereference numbers are carried forward from FIG. 2 a to FIG. 2 b toindicate like features. Further, therefore, transmitter 12′ also may beused for either or both of base stations BST1 and BST2 in FIG. 1, wheretransmitter 12′ also provides an interference-limited system that isimproved as a whole due to the inclusion within transmitter 12′ of thefunctionality to retransmit symbols, as a group in the form of a packet,as part of a HARQ operation performed by a corresponding receiver.

Transmitter 12′ differs from transmitter 12 in that transmitter 12′ isgenerally a multiple-input multiple-output (“MIMO”) system, meaningtransmitter 12′ has at least two or more transmit antennas fortransmitting to a receiver, where there is no redundancy between symbolstransmitted by different ones of the transmit antennas. Looking morespecifically in this regard to FIG. 2 b, again the output of symbolmapper 18 provides a stream of symbols x_(i). However, these symbols areconnected as an input to a serial-to-parallel converter 21.Serial-to-parallel converter 21, therefore, outputs parallel streams ofsymbols to each of its transmit antennas. In the example of FIG. 2 b,two such transmit antennas TAT₁′ and TAT₂′ are shown and, thus,serial-to-parallel converter 21 outputs two such streams. For example,for a stream of symbols x₁, x₂, x₃, x₄ input to serial-to-parallelconverter 21, it outputs symbols x₁ and ₃ to transmit antenna TAT₁′ andit outputs symbols x₂ and x₄ to transmit antenna TAT₂′. Thus, oneskilled in the art will appreciate that there is no symbol redundancy asbetween the symbol stream on transmit antenna TAT₁′ and the symbolstream on transmit antenna TAT₂′. In addition, however, symbolstransmitted along one transmit antenna may interfere with symbolstransmitted along the other transmit antenna and, thus, transmitter 12′is part of an interference-limited system.

FIG. 3 illustrates an electrical and functional block diagram of areceiver 30 ₁ according to the preferred embodiment and for receivingsignals from transmitter 12 of FIG. 2 a or transmitter 12′ of FIG. 2 b.Receiver 30 ₁ includes a total of Q receive antennas RAT₁ throughRAT_(Q), where the actual value of Q may be one or greater, such asdiscussed in the above-incorporated U.S. patent application Ser. No.10/107,275 (docket: TI-32842) and also based on the type of transmitter(e.g., STTD, OTD, MIMO, and so forth). Note that each receive antennaRAT_(x) receives a signal from each of the P transmit antennas TAT₁through TAT_(P). For the sake of convention, let each of the receivedsignals be indicated as r_(q) for each q^(th) of the Q receive antennasand, thus, for a number Q of symbol samples received at a time (n), thena vector r of the received signals across all Q receive antennas may bedefined as in the following Equation 2:

$\begin{matrix}{{r(n)} = \begin{bmatrix}{r_{1}(n)} \\\vdots \\{r_{Q}(n)}\end{bmatrix}} & {{Equation}\mspace{14mu} 2}\end{matrix}$While not shown, receiver 30 ₁ preferably includes an appropriate radiofrequency interface coupled to each receive antenna. Further, withrespect to the received vector r, receiver 30 ₁ also includes sufficientsampling circuitry to sample the received input signals across anappropriate amount of time or space based upon the type of transmitterformat. Thus, the received signal vector over a period of time such asencompassing an entire symbol or multiple symbols may be referred tomore generally as r. For example, if transmitter 12 or 12′ provides aCDMA signal, then receiver 30 ₁ correspondingly includes sufficientcircuitry directed to CDMA signals, including sample collectioncircuitry for collecting a sufficient number of chip (or sub-chip)samples corresponding to the desired number of received symbols and alsoto properly remove the spreading code (i.e., to despread) from thesymbols at some point in the receiver processing structure. As anotherexample, if transmitter 12 or 12′ provides a TDMA signal, then receiver30 ₁ correspondingly includes sufficient circuitry directed to TDMAsignals, including sample collection circuitry for collecting a timeslot (or sub-slot) samples corresponding to the desired number ofreceived symbols. As still another example, if transmitter 12 or 12′provides a MIMO signal, then the extent of sampling symbol may depend onwhether the transmitter is a spread spectrum transmitter and, hence,akin to CDMA in which case chip or sub-chip sampling is likely to beimplemented or whether the transmitter is akin to TDMA in which caseslot or sub-slot sampling is to be expected. In any event, the preferredembodiments contemplate accommodating any of these examples, where theremaining signal processing and functionality is necessarily adapted tothe corresponding number of processed samples.

Each receive antenna RAT₁ through RAT_(Q) also provides pilot symbols toa channel estimator 32. These pilot symbols are typically communicatedin a separate channel such as the known common pilot channel (“CPICH”),or alternatively, pilot symbols could be included in the same channel asthe data symbols. In either approach, in response to the pilot symbols,channel estimator 32 estimates, from the received pilot symbols, achannel effect estimate matrix designated herein as H. Morespecifically, as the signals are transmitted by transmitter 12 or 12′ toreceiver 30 ₁, those signals are influenced by the so-called channeleffect between transmitter 12 or 12′ to receiver 30 ₁. Accordingly, inan effort to remove this influence from the received signals, thatchannel effect is estimated in the form of the matrix H. To furtherappreciate H, note that the vector r may be written in the followingEquation 3 form, where Equation 3 is further written in terms of thetransmitted symbol vector s:r=Hs+w  Equation 3From Equation 3, one skilled in the art will appreciate that r is afunction of the channel matrix H, the transmitted symbols s, and a noisevector w.Equation 3 may be written more precisely now as directed to thepreferred embodiments. Specifically, by way of introduction and per thepreferred embodiment, receiver 30 ₁ serves to accumulate signalscorresponding to an original transmission and retransmissions fromtransmitter 12 or 12′. In other words, in the preferred embodiment,receiver 30 ₁ is operable to perform a type of ARQ operation, where inresponse to detecting an error such as a CRC error, receiver 30 ₁ sendsa wireless feedback signal to transmitter 12 or 12′ which promptstransmitter 12 or 12′ to retransmit the symbol packet that was deemed tobe in error when received. Upon receipt of one or more retransmissions,receiver 30 ₁ accumulates each of the received signals corresponding tothose retransmissions. Thus, the accumulation of each retransmissionlater provides the basis to provide symbol detection based on multipleretransmissions, thereby providing a HARQ or HARQ-like functionality inan interference-limited system. Looking then at Equation 3, and for sakeof a reference for each re-transmission, let the subscript “(i)”indicate that a corresponding signal or vector is for the i^(th)retransmission of a same data from transmitter 12 or 12′; thus, Equation3 may be written in the following form of Equation 3.1:r _((i)) =H _((l)) s+w _((i))  Equation 3.1In Equation 3.1, H_((i)) is the QxP channel matrix experienced by thedata at the i^(th) transmission, and s is the same symbol vector eithertransmitted once originally or as the same vector for each of the Iretransmissions. In all events, from the known values of the pilotsymbols, channel estimator 32 determines the difference between thoseknown values and the values corresponding to those pilot symbols asreceived in the vector r, from which the channel matrix H is estimated.This estimate H is connected from channel estimator 32 as an input to aconjugate transpose determination block 34 and as a multiplicand inputto multiplier 36, as further discussed below.

Conjugate transpose determination block 34 performs as its namesuggests, that is, using known matrix principles it determines theconjugate transpose of its matrix input; in the present instance,therefore, it determines the conjugate transpose of the channel estimatematrix H. For the sake or reference in this document, such a conjugatetranspose is hereafter designated as H^(H). The value of H^(H) is outputfrom conjugate transpose determination block 34 as a multiplicand inputto multiplier 36 and also to a matched filter 38. Multiplier 36determines the product of its two multiplicand inputs and, thus, itoutputs the value of H^(H)H. This product is provided as an input to achannel product matrix accumulator 42, as detailed later.

Looking to matched filter 38, in addition to receiving H^(H) fromconjugate transpose determination block 34, matched filter 38 alsoreceives the vector r from receive antennas RAT₁ through RAT_(Q). Thus,matched filter 38 includes collection circuitry for collecting a numberof signal samples for a number of successive time instances and fromeach of the plurality of receive antennas so as to represent r, aspertaining to either an original transmission, or later as to each ofany of the I retransmissions. In response to its input, matched filter38 performs a function known in the art to multiply its two inputs, afirst representing the received signals and a second that, whenmultiplied the first, provides an output that effectively increases ormaximizes the signal-to-noise ratio in the output signal; in the presentcase, the second factor is the conjugate transpose of the channelestimate matrix H, herein shown as H^(H), and the multiplication of thefirst and second factors thereby produce an output vector y as shown inthe following Equation 4:y=H ^(H) r  Equation 4Note also that the term matched filter is not intended to be limiting,as other names such as rake combining or maximal ratio combining alsoare sometimes used in the art to include the same functionality ofmaximizing the signal to noise ratio in the received input signal byequivalently processing that signal in view of a factor that relates tothe channel effect. Lastly, the output of matched filter 38 is connectedas an input to a retransmission accumulator 40.

Recalling from the previous introduction that receiver 30 ₁ preferablyis operable to perform a type of HARQ functionality, in more detail itwill now be presented how upon receipt of one or more retransmissions,retransmission accumulator 40 accumulates each of the received signalscorresponding to those retransmissions, as those signals are alsoprocessed through matched filter 38. Thus, the accumulation of eachretransmission later provides the basis to provide symbol detectionbased on multiple retransmissions, thereby providing a HARQ or HARQ-likefunctionality in an interference-limited system. Looking then in greaterdetail at retransmission accumulator 40, the vector signal y frommatched filter 38 is connected as an input to an adder 40 ₁, and againthe subscript “(i)” indicates that the vector y_((i)) is for the i^(th)retransmission of a same data from transmitter 12 or 12′; thus, each ofthe first transmission, and any later I retransmissions of the samedata, sent in response to a detected error by receiver 30 ₁ and acorresponding request for retransmission, shall be one of a total of I+1total transmissions of the same packet of data. The output of adder 40 ₁passes through a delay block 40 ₂ to a buffer 40 ₃. Note that delayblock 40 ₂ is included to suggest that there is anticipated some delayin the operation of accumulator 40 as it awaits receipt of subsequentretransmissions from transmitter 12 or 12′. In any event, the output ofbuffer 40 ₃ is connected as an addend input to adder 40 ₁. Looking thenat the general operation of accumulator 40, note that for the first ofthe I+1 transmissions (i.e., the original or first transmission), itpasses through delay block 40 ₂ and is stored in buffer 40 ₃. For afirst retransmission of (i)=1, then that first retransmission isprocessed through matched filter 38; accordingly, the output of matchedfilter 38 may be stated according to the following Equation 5:y _((i)) =H ^(H) _((i)) r _((i))   Equation 5This output, y_((i)), is then summed by adder 40 ₁ with the value of ycorresponding to the first transmission and that was previously storedin buffer 40 ₃. That sum again incurs a delay 40 ₂ and is stored inbuffer 40 ₃, thereby overwriting the previous sum stored therein. Fromthe preceding, one skilled in the art will appreciate that this processmay repeat for numerous retransmissions, whereby ultimately the finalI+1 transmission is added by adder 40 ₁ to the accumulationcorresponding to the previous I transmissions, thereby presenting aresulting output indicated herein and in FIG. 3 as {tilde over (y)}_(l),and the value of {tilde over (y)}_(i) is connected to an interferencesuppression block 44.

Interference suppression block 44, in addition to receiving {tilde over(y)}_(l) from retransmission accumulator 40, also receives anaccumulated channel product matrix C_(l) from channel product matrixaccumulator 42. Looking in more detail to channel product matrixaccumulator 42, note that it includes blocks comparable toretransmission accumulator 40, but accumulator 42 is directed to thechannel estimate that corresponds to each retransmission. Specifically,recall that multiplier 36 provides the value H^(H)H to channel productmatrix accumulator 42. This value is connected as an addend to an adder42 ₁, and for sake of consistency and given that channel product matrixaccumulator 42 accumulates in a comparable manner as the accumulation ofretransmission accumulator 40, then note that the value H^(H)H actuallycorresponds to that product as determined for either a firsttransmission or one of the I retransmissions; hence, consistent with theabove, the “(i)” subscript is added to the product, thereby yielding anindication of H_((i)) ^(H)H_((i)). Accordingly, for a given firsttransmission or a retransmission of that first transmission, let thisproduct be referred to in this document as the channel product matrixand be as shown in the following Equation 6:C _((i)) =H ^(H) _((i)) H _((i))   Equation 6Note that the term “channel product matrix” is used in the sense thatthe product of Equation 6 represents generally what may be removed fromthe output of matched filter 38 so as to recover the symbols, s,therein. Specifically, the signal output from matched filter 38represents the received vector r multiplied times H^(H) (i.e., asH^(H)r), and ignoring noise, and since r as shown in Equation 3 includesthe term Hs, then the signal output from matched filter 38 alsorepresents H^(H)HS. Thus, to recover s and for now also ignoring theeffect of interference, then the product H^(H)H may be multiplied timesthe output H^(H)Hs of matched filter 38 in an effort to recover s.

The output of adder 42 ₁ passes through a delay block 42 ₂ to a buffer42 ₃, and note that delay block 42 ₂ is included to suggest that thereis anticipated some delay in the operation of accumulator 42 as itawaits receipt of the channel estimates and products corresponding tosubsequent retransmissions from transmitter 12 or 12′. The output ofbuffer 42 ₃ is connected as an addend input to adder 42 ₁. Looking thenat the operation of accumulator 42, it operates in a comparable mannerto accumulator 40, but with respect to accumulating each value C_((i))corresponding to the I+1 retransmissions (and receipt by receiver 30 ₁)of a same packet. For a first retransmission of (i)=1, then C₍₁₎ issummed by adder 42 ₁ with the value of H^(H)H that corresponded to thefirst transmission, where that earlier value of H^(H)H was previouslystored in buffer 42 ₃. That sum again incurs a delay 42 ₂ and is storedin buffer 42 ₃, thereby overwriting the previous sum stored therein.From the preceding, one skilled in the art will appreciate that thisprocess may repeat for numerous retransmissions, whereby ultimately thefinal C_((I+1)) value is added by adder 42 ₁ to the accumulationcorresponding to the previous I retransmissions and the firsttransmission, thereby presenting a resulting output indicated herein andin FIG. 3 as C_(l), and that value of C_(l) is connected to interferencesuppression block 44.

Interference suppression block 44 includes sufficient circuitry toreduce the effects of interference that are included within the receivedsignal, where as shown above the input signal {tilde over (y)}_(l)represents the accumulation of I+1 transmissions of a same packet due toa detected error (e.g., CRC) in that packet. In general, FIG. 3illustrates this functionality as a function F[.]. This designation isintended to depict that, as known in the art, interference reduction orsuppression may be achieved using numerous different functions orapproaches, as discussed below. However, before discussing thoseapproaches, note the preferred embodiment contrasts with the prior art.For example, prior art HARQ systems do not include interferencesuppression because those systems have not been implemented withinterference-limited techniques (e.g., CDMA, TDMA, MIMO). Further,therefore, the prior art use of interference suppression has not been inconnection with HARQ and when used has related to a single transmissionof a signal and some channel effect parameter corresponding to thatsingle transmission of a signal. In contrast, as shown above,interference suppression block 44 receives and operates with respect toan accumulated signal {tilde over (y)}_(i) and an accumulated channelproduct matrix, C_(i). Thus the functionality of interferencesuppression block 44 in determining the cumulative soft decisionstatistics after N transmissions may be stated generally as in thefollowing Equation 6.1, where N is also used added to scale eachaccumulated value:

$\begin{matrix}{{F\left\lbrack {{\overset{\sim}{y}}_{i},C_{i}} \right\rbrack} = {F\left\lbrack {{\frac{1}{N}{\sum\limits_{i = 1}^{N}\; y_{(i)}}},{\frac{1}{N}{\sum\limits_{i = 1}^{N}\; C_{(i)}}}} \right\rbrack}} & {{Equation}\mspace{20mu} 6.1}\end{matrix}$Note that the actual value of the accumulated value of C_(l) also may bescaled, such as by multiplying it times 1/I+1, where recall that thedenominator of that fraction is the total number of transmissionsincluding the first and all I retransmissions of a given packet.Further, by using this factor, note that the effects of differentscenarios are comprehended. In other words, the channel matrix H_((i))can be the same or different for the first transmission and everyretransmission and, hence, the same is true for each value C_((i)). Forexample, in fast fading scenarios, H_((i)) is uncorrelated withH_((l+1)). This results in what may be analogized to an effective timediversity gain upon retransmissions. For slow fading of quasi-staticchannels, H_((i))=H, and for these instances there are techniques thatcan be used to induce “artificial” fast fading, such as described inU.S. patent application Ser. No. 10/230,003, filed Aug. 28, 2002, andherein incorporated herein by reference.

Completing the discussion of interference suppression block 44, it mayimplement one of many known approaches to suppressing interference,where those approaches are modified in that the accumulated channelproduct matrix C_(l) is used by block 44. Such approaches for block 44include: (i) zero forcing or minimum mean square error (“MMSE”); (ii)1-shot (i.e., linear) or iterative; (ii) 1-stage or multistage; and (iv)maximum likelihood detection. Certain of these techniques also may becombined, as is known, such as with a linear MMSE, an iterative MMSE, alinear zero forcing, and an iterative zero forcing. Although aniterative receiver may tend to outperform linear receivers due to thereduced noise enhancement and higher diversity gain, the iterativeapproach may suffer from error propagation especially for lowsignal-to-noise ratio. Preferably, however, this can be reducedconsiderably by ordering the detection, where the largestsignal-to-interference plus noise ratio is detected at each iteration.Further, each of the preceding approaches may be implemented in variousmanners. For example, a linear equalizer can be implemented usingmultiple-input multiple-output FIR filtering. As another example, alinear approach can be implemented using a series of multiple-inputmultiple-output FIR filtering operations. As still another example,equalizer taps also can be trained using adaptive filtering techniques,as may be ascertained by one skilled in the art. In any event, theoutput of interference suppression block 44 represents a soft estimateof the symbol vector s, and this estimate is referred to herein andshown in FIG. 3 as {tilde over (z)}_(l). Accordingly, the relationshipof the input and output to interference suppression block 44 may bestated according to the following Equation 7:{tilde over (z)} _(l) =F[{tilde over (y)} _(l) ,C _(i)]  Equation 7

The function F[.] in Equations 6.1 and 7 may be further illustrated byways of example, as are now shown for the two alternatives whereininterference suppression block 44 is implemented using a linear zeroforcing function or where interference suppression block 44 isimplemented using linear MMSE. In the case of interference suppressionblock 44 as linear zero forcing function, then Equation 6.1 may bewritten as the following Equation 7.1:F[{tilde over (y)} _(i) , C _(i) ]=C _(i) ⁻¹ {tilde over (y)} _(i)  Equation 7.1For linear zero forcing, therefore, Equation 7.1 may be expanded suchthat the soft symbol decision can be written as in the followingEquation 7.2, where as in Equation 6.1 N is the number of transmissionsand is used as a factor to scale each accumulated value:

$\begin{matrix}{{F\left\lbrack {{\overset{\sim}{y}}_{i},C_{i}} \right\rbrack} = {\left. {C_{i}^{- 1}{\overset{\sim}{y}}_{i}}\Rightarrow{\left( {\frac{1}{N}{\sum\limits_{i = 1}^{N}\; C_{(i)}}} \right)^{- 1}\left( {\frac{1}{N}{\sum\limits_{i = 1}^{N}\; y_{(i)}}} \right)} \right. = {\left( {\sum\limits_{i = 1}^{N}\; C_{(i)}} \right)^{- 1}{\sum\limits_{i = 1}^{N}\; y_{(i)}}}}} & {{Equation}\mspace{20mu} 7.2}\end{matrix}$In the case of interference suppression block 44 as linear MMSEfunction, then Equation 6.1 may be written as the following Equation7.3:F[{tilde over (y)} _(i) , C _(l)]=(C _(l)+μΛ⁻¹)⁻¹ {tilde over (y)}_(l)  Equation 7.3In Equation 7.3, μ>0 is the appropriate noise variance, while Λ is amatrix having diagonals equal to signal powers {λ₁, λ₂, . . . , λ_(P)},for the P transmit antennas given an assumption of symbol independenceand an expected value of E[ss^(H)]={λ₁, λ₂, . . . , λ_(P)}. FromEquation 7.3, note that the specific example of linear MMSE both furtherinvolves the terms

$\mu = {\frac{\sigma^{2}}{N} > 0}$and Λ and, thus, FIG. 3 further illustrates these terms as possibleinputs to interference suppression block 44, using a dotted line todemonstrate that such inputs are used for the present example. Thus,interference suppression block 44 not only operates with respect to anaccumulated signal {tilde over (y)}_(l) and an accumulated channelproduct matrix, C_(l), it is further responsive to these additionalinputs for this example. Concluding linear MMSE, Equation 7.3 may beexpanded such that the soft symbol decision can be written as in thefollowing Equation 7.4, where again a factor relating to the Ntransmissions is also added to scale each accumulated value:

$\begin{matrix}{\left. {F\left\lbrack {{\overset{\sim}{y}}_{i},C_{i}} \right\rbrack}\Rightarrow{\left( {{\frac{1}{N}{\sum\limits_{i = 1}^{N}\; C_{(i)}}} + {\frac{\sigma^{2}}{N}\Lambda^{- 1}}} \right)^{- 1}\left( {\frac{1}{N}{\sum\limits_{i = 1}^{N}\; y_{(i)}}} \right)} \right. = {\left( {{\sum\limits_{i = 1}^{N}\; C_{(i)}} + {\sigma^{2}\Lambda^{- 1}}} \right)^{- 1}\left( {\sum\limits_{i = 1}^{N}\; y_{(i)}} \right)}} & {{Equation}\mspace{20mu} 7.4}\end{matrix}$Lastly, one skilled in the art may derive the implementations for theother alternatives set forth above for interference suppression block44.

The soft estimates {tilde over (z)}_(l) are connected to the remainingcircuitry in receiver 30 ₁, which may be constructed and operateaccording to known principles. Thus, {tilde over (z)}_(l) is connectedto a demodulator 46, which removes the modulation imposed on the signalby symbol mapper 18 of transmitter 12 or 12′ and thereby outputs encodedbit probabilities, which are generally equivalent to soft encoded bitestimates. The output of demodulator 46 is connected to a deinterleaver48, which performs an inverse of the function of interleaver 16 oftransmitter 12 or 12′, and the output of deinterleaver 48 is connectedto a channel decoder 50. Channel decoder 50 may include a Viterbidecoder, a turbo decoder, a block decoder (e.g., Reed-Solomon decoding),or still other appropriate decoding schemes as known in the art. In anyevent, channel decoder 50 further decodes the data received at itsinput, typically operating with respect to certain error correctingcodes, and it outputs a resulting stream of estimated decoded bits.Indeed, note that the probability of error for data input to channeldecoder 50 is far greater than that after processing and output bychannel decoder 50.

The decoded symbols are output from channel decoder 50 to a packet errorcheck block 52 which, as discussed earlier, in one preferred embodimentis a CRC error check block. Block 52 performs as known in the art, thatis, it examines the CRC code as corresponding to a packet of bits, wherethat packet includes numerous symbols. If the CRC code indicates anerror in the packet, then block 52 transmits a signal, via a wirelessfeedback channel illustrated by a dotted line, to transmitter 12 or 12′.As discussed above, in response to this communication, transmitter 12 or12′ will retransmit the packet and, hence, its corresponding symbols,and that retransmission will be processed as described above. Suchretransmission requests will continue until either no CRC error is foundor until some maximum threshold number of retransmissions have beenrequested. Once all retransmissions are complete, then a correspondingset of decoded symbols are provided by channel decoder 50 and thenpassed to block 52. Finally, the decoded symbol stream output by block52 may be received and processed by additional circuitry in receiver 30₁, although such circuitry is not shown in FIG. 3 so as to simplify thepresent illustration and discussion.

FIG. 4 illustrates an electrical and functional block diagram of areceiver 30 ₂ as an alternative preferred embodiment for receivingsignals from transmitter 12 of FIG. 2 a or transmitter 12′ of FIG. 2 b.Receiver 30 ₂ includes certain of the same features as receiver 30 ₁described above with respect to FIG. 3 and for those features likereference numbers are used in both FIGS. 3 and 4. Additionally, sincethese features are detailed above, the reader is assumed familiar withthose details and they are not repeated at the same level of detail inthe following discussion of receiver 30 ₂. Generally, therefore,receiver 30 ₂ includes a number Q of receive antennas RAT₁ throughRAT_(Q), and the signals r_((i)) from those antennas are connected via aradio frequency interface (not shown) to a channel estimator 32 and amatched filter 38. Channel estimator 32 provides its channel estimate,H, as an input to a conjugate transpose determination block 34 and as amultiplicand input to multiplier 36. Conjugate transpose determinationblock 34 determines the conjugate transpose of its matrix input, H, andthe resultant output, H^(H), is connected as a multiplicand input tomultiplier 36 and also to matched filter 38. Multiplier 36 determinesthe product of its two multiplicand inputs and, thus, it outputs thevalue of H^(H)H, where recall from Equation 6 that this product isdesignated as C_((i)). Additional connections and functionality, andparticularly as directed to differences between receivers 30 ₂ and 30 ₁,are described below.

Matched filter 38 of receiver 30 ₂ provides an output y_((i)) asdescribed with respect to receiver 30 ₁, but in the case of receiver 30₂ the value y_((i)) is connected as an input to an interferencesuppression block 60. Interference suppression block 60 also receivesthe value C_((i)) from multiplier 36.

Interference suppression block 60 includes sufficient circuitry toreduce the effects of interference that are included within the receivedsignal, and in general FIG. 4 illustrates this functionality as afunction F[.] to depict that, like block 44 in FIG. 3, againinterference reduction or suppression may be achieved using numerousdifferent approaches, as discussed above (e.g., (i) zero forcing orMMSE; (ii) 1-shot (i.e., linear) or iterative; (iii) 1-stage ormultistage; (iv) maximum likelihood detection; (v) combination ofapproaches (i) through (iv)). For receiver 30 ₂, as was the case alsofor receiver 30 ₁, this alternative preferred embodiment also contrastswith the prior art in that prior art HARQ systems do not includeinterference suppression because those systems have not been implementedwith interference-limited techniques (e.g., CDMA, TDMA, MIMO). Theoperation of interference suppression block 60 is generally as suggestedby its name, that is, to operate with respect to its inputs to suppressthe effects of interference in the received input signal y_((i)), wherethe specific operation is based on the type of interference suppressionapproach. In all approaches, however, note that the suppression forreceiver 30 ₂ is performed individually for each of the originaltransmission of a packet as well as for each of the I retransmissions ofthat packet; mathematically, this aspect is illustrated in thatinterference suppression block 60 operates with respect to each pair ofsignals y_((i)) and C_((i)), for a given transmission or retransmissionof a same packet. Thus, this is in contrast to the alternative preferredembodiment receiver 30 ₁ of FIG. 3, which performs its interferencesuppression only after each signal from the matched filter is separatelyaccumulated, as is each channel product matrix signal from multiplier36. Thus the functionality of interference suppression block 60 indetermining the cumulative soft decision statistics after Ntransmissions may be stated generally as in the following Equation 7.5,where again the factor N is added to scale each accumulated value:

$\begin{matrix}{\frac{1}{N}{\sum\limits_{i = 1}^{N}{F\left\lbrack {y_{(i)},C_{(i)}} \right\rbrack}}} & {{Equation}\mspace{14mu} 7.5}\end{matrix}$In addition, the post-processing following interference suppressionblock 60 differs from the prior art as well as from receiver 30 ₁, asfurther described below. Returning to receiver 30 ₂ of FIG. 4, eachoutput corresponding to a received and processed retransmission isdesignated z_((i)), where i is one of the I retransmissions. This outputsignal, z_((i)), is connected to a retransmission accumulator 62.

Before discussing retransmission accumulator 62, note that the functionF[.] for interference suppression block 60 may be illustrated also byways of example using the same two alternatives that were describedearlier with respect to interference suppression block 44, namely, usinga linear zero forcing function or using linear MMSE, but here note thateach received set of inputs to interference suppression block 60corresponds only to the I^(th) re-transmission. In the case ofinterference suppression block 60 as linear zero forcing function, thenthe terms of Equation 7.5 may be expressed as shown in the followingEquation 7.6 for the linear zero forcing function:

$\begin{matrix}\left. {\frac{1}{N}{\sum\limits_{i = 1}^{N}{F\left\lbrack {y_{(i)},C_{(i)}} \right\rbrack}}}\Rightarrow{\frac{1}{N}{\sum\limits_{i = 1}^{N}{C_{(i)}^{- 1}y_{(i)}}}} \right. & {{Equation}\mspace{14mu} 7.6}\end{matrix}$In the case of interference suppression block 60 as linear MMSEfunction, then Equation 7.5 may be written as the following Equation7.7:F[y _((l)) , C _((l))]=(C _((l))+μΛ⁻¹)⁻¹ y _((l))  Equation 7.7Concluding linear MMSE, Equation 7.7 may be expanded such that the softsymbol decision can be written as in the following Equation 7.8, whereagain a factor relating to the N transmissions is also added to scaleeach accumulated value:

$\begin{matrix}\left. {\frac{1}{N}{\sum\limits_{i = 1}^{N}{F\left\lbrack {y_{(i)},C_{(i)}} \right\rbrack}}}\Rightarrow{\frac{1}{N}{\sum\limits_{i = 1}^{N}{\left( {C_{(i)} + {\sigma^{2}\Lambda^{- 1}}} \right)^{- 1}y_{(i)}}}} \right. & {{Equation}\mspace{14mu} 7.8}\end{matrix}$From Equation 7.8, note that the specific example of linear MMSE furtherinvolves the terms μ=σ²>0 and Λ and, thus, FIG. 4 further illustratesthese terms as possible inputs to interference suppression block 60,using a dotted line to demonstrate that such inputs are used for thepresent example.

Retransmission accumulator 62 receives the signal, z_((i)), and it isconnected as an addend input to an adder 62 ₁. The output of adder 62 ₁passes through a delay block 62 ₂ to a buffer 62 ₃. Delay block 62 ₂ isincluded to suggest that there is anticipated some delay in theoperation of accumulator 62 as it, as part of receiver 30 ₂, awaitsreceipt of subsequent retransmissions from transmitter 12 or 12′. Theoutput of buffer 62 ₃ is connected as an addend input to adder 62 ₁.Looking then at the general operation of retransmission accumulator 62,first recall that for all of the I+1 transmissions, interferencesuppression block 60 suppresses interference in the re-transmittalsignal, with the result, z_((i)), provided to retransmission accumulator62. Accordingly, retransmission accumulator 62 accumulates thesuppression achieved for each of the I+1 transmissions, where thisoperation provides a result {tilde over (z)}_(l) that may therefore bestated as shown in the following Equation 8:

$\begin{matrix}{{\overset{\sim}{z}}_{i} = {{\sum\limits_{i = 1}^{I + 1}z_{(i)}} = {\sum\limits_{i = 1}^{I + 1}{F\left\lbrack y_{(i)} \right\rbrack}}}} & {{Equation}\mspace{14mu} 8}\end{matrix}$From Equation 8, and recalling that the value F[y_((l))] includes, foreach of the I+1 transmissions, the value C_((i)), then each valuez_((i)) reflects an accumulation of each value C_((i)) insofar as it isincluded in F[y_((l))]. Thus, each accumulated value of z_((i)) also maybe scaled, such as by multiplying it times 1/I+1. In any event, theoutput {tilde over (z)}_((i)) of retransmission accumulator 62represents a soft estimate of the symbol vector s. The soft estimate{tilde over (z)}_(l) is connected to the remaining circuitry in receiver30 ₂, which may be constructed and operate according to knownprinciples.

FIG. 5 illustrates a receiver 30 ₂′ as yet another alternative preferredembodiment for receiving signals from transmitter 12 of FIG. 2 a ortransmitter 12′ of FIG. 2 b. Receiver 30 ₂′ of FIG. 5 shares many of thesame blocks as receiver 30 ₂ of FIG. 4 and, thus, like reference numbersare carried forward for such blocks from FIG. 4 to FIG. 5 and the readeris assumed familiar with those blocks so the previous discussionregarding them is not repeated below. By way of contrast, however,receiver 30 ₂′ illustrates the example mentioned above wherein theinterference suppression technique employed is maximum likelihood. Asknown in the art, the maximum likelihood technique effectively combinesthe operations of interference suppression and demodulation in order todirectly produce bit probabilities; in this regard, note therefore thatreceiver 30 ₂′ includes a bit probability block 64 in place of anindividual interference suppression block, and the bit probability block64 therefore operates jointly as opposed to the preceding examples wheresymbol probabilities are first determined followed by demodulation. Alsoin this regard, therefore, the later stage of demodulation 46 fromprevious embodiments is not separately shown in FIG. 5, as that functionis encompassed within bit probability block 64. In other words,therefore, bit probability block 64 comprises both an interferencesuppression and demodulation function. The remaining operation ofreceiver 30 ₂′ will therefore be readily ascertainable by one skilled inthe art. Further, this illustration of an implementation of interferencesuppression as part of the bit probability function also may be readilyapplied to receiver 30 ₁ of FIG. 3.

From the above, it may be appreciated that the above embodiments providean interference-limited wireless communication system with packetretransmission in response to detected packet error, where signals fromthe retransmitted packets are accumulated so as to improve symbol softestimates. Two preferred receivers 30 ₁ and 30 ₂ are described, wheregenerally it may be observed that receiver 30 ₁ accumulates eachreceived signal and a corresponding channel product matrix and thenperforms interference suppression on the accumulated totals, whilereceiver 30 ₂ performs interference suppression with respect to eachindividual signal corresponding to a retransmission along with acorresponding channel product matrix and then accumulates the total ofeach interference suppression. Selection of each different receiver maybe based on various design criteria, including whether the expectedchannel is fast fading or quasi-static. Further, the two differentreceivers 30 ₁ and 30 ₂ will have different buffering requirements,which also may impact a selection as between the two. More particularly,while both receivers store data for each of the I+1 transmissions of apacket, a higher number of A/D bits may be required for storing theinput to interference suppression block 44 of receiver 30 ₁ as comparedto the buffering of the accumulations for retransmission accumulator 62,because the former is likely to require a greater data resolution inorder to compute considerable matrix operations and achieve fixed pointresolution, thereby necessitating a greater number of input bits. In anyevent, each approach provides various benefits over the prior art.Further, while the present embodiments have been described in detail,various substitutions, modifications or alterations could be made to thedescriptions set forth above without departing from the inventive scopewhich is defined by the following claims.

1. A wireless receiver for receiving signals from a transmittercomprising at least one transmit antenna in a wireless system, whereinthe signals comprise a plurality of symbols and wherein each symbol inthe plurality of symbols corresponds to a number of bits, the receivercomprising: a plurality of receive antennas; collection circuitry,coupled to the plurality of receive antennas, for collecting a pluralityof signal samples from the plurality of receive antennas, wherein theplurality of signal samples comprise at least one symbol andinterference effects and correspond to each packet in a number I+1 ofpackets transmitted by the transmitter, wherein each packet of thenumber I+1 of packets as transmitted by the transmitter comprise atleast a portion of a same set of symbols and are re-transmitted by thetransmitter in response to a request from the receiver; suppressioncircuitry, coupled to the collection circuitry, for suppressing theinterference effects in the number I+1 of packets; circuitry foraccumulating a result corresponding to each packet of the number I+1 ofpackets, wherein the result corresponds to an output of the collectioncircuitry, and for the accumulating either prior to or after theoperation of said suppression circuitry; circuitry responsive to signalsfrom the suppression circuitry and for providing estimates of a group ofbits; detection circuitry for detecting an error in a packet thatcomprises the group of bits; circuitry for sending the request to thetransmitter to transmit a retransmission of a packet in response to thedetection circuitry detecting the error; and circuitry, coupled to theplurality of receive antennas, for determining a channel estimatematrix; and wherein the circuitry for accumulating is coupled betweenthe collection circuitry and the suppression circuitry; and wherein thesuppression circuitry is responsive to the accumulated resultscorresponding to each packet of the number I+1 of packets.
 2. Thereceiver of claim 1 and further comprising circuitry, coupled to theplurality of receive antennas, for determining a channel estimatematrix.
 3. The receiver of claim 2: wherein the plurality of symbolscomprises pilot symbols; and wherein the circuitry for determining achannel estimate matrix determines the channel estimate matrix inresponse to the pilot symbols.
 4. The receiver of claim 2 and furthercomprising circuitry for increasing the signal to noise ratio of thereceived signals in response to the channel estimate matrix.
 5. Thereceiver of claim 2 and further comprising circuitry for increasing thesignal to noise ratio of the received signals in response to a conjugatetranspose of the channel estimate matrix.
 6. The receiver of claim 2:and further comprising circuitry for determining a plurality of channelestimate matrices; and wherein each channel estimate matrix in theplurality of channel estimate matrices corresponds to a respectivepacket in the number I+1 of packets transmitted by the transmitter. 7.The receiver of claim 6 wherein the circuitry for determining aplurality of channel estimate matrices produces a result correspondingto each packet of the number I+1 of packets by multiplying the receivedsignals corresponding to each packet of the number I+1 of packets timesa respective conjugate transpose of the channel estimate matrixcorresponding to each packet of the number I+1 of packets.
 8. Thereceiver of claim 7 and further comprising circuitry for determining aproduct corresponding to each packet of the number I+1 of packets bymultiplying a conjugate transpose of the channel estimate matrixcorresponding to each packet of the I+1 packets times a respectivechannel estimate matrix corresponding to each packet of the number I+1of packets.
 9. The receiver of claim 8 and further comprising circuitryfor accumulating the product corresponding to each packet of the numberI+1 of packets.
 10. The receiver of claim 9 wherein the suppressioncircuitry is further responsive to the accumulated products.
 11. Thereceiver of claim 9 wherein the suppression circuitry is selected from agroup consisting of zero forcing, minimum mean square error, iterative,and maximum likelihood detection.
 12. The receiver of claim 9: whereinthe suppression circuitry comprises maximum likelihood detectioncircuitry; and further comprising circuitry for determining encoded bitprobabilities from which the estimates of a group of bits aredetermined.
 13. The receiver of claim 9: wherein the suppressioncircuitry provides a corresponding output signal responsive to theaccumulated products and the accumulated results; and wherein thecircuitry for requesting is responsive to the output signal.
 14. Thereceiver of claim 6 wherein the suppression circuitry suppresses theinterference effects in each individual one of each result correspondingto each packet of the number I+1 of packets.
 15. The receiver of claim14: and further comprising circuitry for determining a productcorresponding to each packet of the number I+1 of packets by multiplyinga conjugate transpose of the channel estimate matrix corresponding toeach packet of the I+1 packets times a respective channel estimatematrix corresponding to each packet of the number I+1 of packets; andwherein the suppression circuitry suppresses the interference effects ineach individual one of each result corresponding to each packet of thenumber I+1 of packets in response to the product corresponding to eachpacket of the number I+1 of packets.
 16. The receiver of claim 15wherein the suppression circuitry is selected from a group consisting ofzero forcing, minimum mean square error, iterative, and maximumlikelihood detection.
 17. The receiver of claim 15: wherein thesuppression circuitry comprises maximum likelihood detection circuitry;and further comprising circuitry for determining encoded bitprobabilities from which the estimates of a group of bits aredetermined.
 18. The receiver of claim 1 wherein the signals from thetransmitter comprise a code division multiple access format.
 19. Thereceiver of claim 1 wherein the signals from the transmitter comprise amultiple-input multiple-output format.
 20. The receiver of claim 1wherein the signals from the transmitter comprise a time divisionmultiple access format.
 21. The receiver of claim 1 and furthercomprising circuitry for receiving signals from the suppressioncircuitry and for providing estimates of the symbols.
 22. The receiverof claim 1 in combination with the transmitter.
 23. A method ofoperating a wireless receiver to receive signals from a transmittercomprising at least one transmit antenna in a wireless system, whereinthe signals comprise a plurality of symbols and wherein each symbol inthe plurality of symbols corresponds to a number of bits, the methodcomprising: collecting a plurality of signal samples from a plurality ofreceive antennas, wherein the plurality of signal samples comprise atleast one symbol and interference effects and correspond to each packetin a number I+1 of packets transmitted by the transmitter, wherein eachpacket of the number I+1 of packets as transmitted by the transmittercomprise at least a portion of a same set of symbols and arere-transmitted by the transmitter in response to a request from thereceiver; suppressing the interference effects in the number I+1 ofpackets; accumulating a result corresponding to each packet of thenumber I+1 of packets, wherein the result corresponds to an output fromthe collecting step, and wherein the accumulating step occurs eitherprior to or after the suppressing step with respect to the number I+1 ofpackets; responsive to signals following the step of suppressing theinterference effects, providing estimates of a group of bits; detectingwhether there is an error in a packet that comprises the group of bits;and in response detecting the error, requesting the transmitter totransmit a retransmission of a packet; and wherein the accumulating stepis done between the collection and suppression steps; and wherein thesuppressing step is further responsive to the accumulated products. 24.The method of claim 23 and further comprising determining a channelestimate matrix in response to signals received from at least onereceive antenna.
 25. The method of claim 24 and further comprisingincreasing the signal to noise ratio of the received signals in responseto a conjugate transpose of the channel estimate matrix.
 26. The methodof claim 24: and further comprising determining a plurality of channelestimate matrices; and wherein each channel estimate matrix in theplurality of channel estimate matrices corresponds to a respectivepacket in the number I+1 of packets transmitted by the transmitter. 27.The method of claim 26 wherein the determining step produces a resultcorresponding to each packet of the number I+1 of packets by multiplyingthe received signals corresponding to each packet of the number I+1 ofpackets times a respective conjugate transpose of the channel estimatematrix corresponding to each packet of the number I+1 of packets. 28.The method of claim 26 and further comprising determining a productcorresponding to each packet of the number I+1 of packets by multiplyinga conjugate transpose of the channel estimate matrix corresponding toeach packet of the I+1 packets times a respective channel estimatematrix corresponding to each packet of the number I+1 of packets. 29.The method of claim 28 and further comprising accumulating the productcorresponding to each packet of the number I+1 of packets.
 30. Themethod of claim 26 wherein the suppressing step suppresses theinterference effects in each individual one of each result correspondingto each packet of the number I+1 of packets.
 31. The method of claim 30:and further comprising determining a product corresponding to eachpacket of the number I+1 of packets by multiplying a conjugate transposeof the channel estimate matrix corresponding to each packet of the I+1packets times a respective channel estimate matrix corresponding to eachpacket of the number I+1 of packets; and wherein the suppressing stepsuppresses the interference effects in each individual one of eachresult corresponding to each packet of the number I+1 of packets inresponse to the product corresponding to each packet of the number I+1of packets.
 32. The receiver of claim 1 wherein the circuitry forsending the request is further for sending to the transmitter anacknowledgement when a packet is successfully detected.